Interpretive Summary: The increase in price of traditional feedstuffs for swine has stimulated interest in alternative ingredients. There is little data available as to the effects of adding fibrous feedstuffs to weanling pig diets. Therefore, an experiment was conducted to determine whether adding fiber to weanling pig diets influences growth performance, markers of inflammation, and the expression of genes involved in intestinal growth. Weanling pigs were subjected to one of four dietary treatments: 1) control diets; 2) diets containing 7.5% dried distillers grains with solubles; 3) diets containing 7.5% soybean hulls; and 4) diets containing 7.5% citrus pulp for 28 days. The type of diet fed had no impact on overall growth performance or overall pig health. Pigs fed diets containing 7.5% dried distillers grains with solubles had increased inflammatory cytokine expression in intestinal tissue. In addition, pigs fed 7.5% soybean hulls had increased intestinal insulin-like growth factor I expression. These findings suggest that feeding 7.5% dried distillers grains with solubles, 7.5% soybean hulls, or 7.5% citrus pulp does not impact growth performance in weanling pigs. However, the addition of dried distillers grains with solubles to weanling pig diets appears to affect intestinal inflammation. The research results described in this report provide researchers at universities, feed companies, allied industries, and swine production facilities data showing that feeding fiber to weanling pigs does not decrease growth performance, but may alter the localized inflammatory response in the gut.

Technical Abstract:
The effects of adding fibrous feedstuffs on growth performance, intestinal cytokine expression, markers of inflammation, abundance of phosphorylated S6 kinase (S6K), and the expression of genes that control intestinal growth was evaluated in weanling pigs. Pigs (n = 120; 5.2 kg and 24 d of age) were randomly assigned to four dietary fiber treatments. The dietary fiber treatments were 1) control diet containing no added fiber source, 2) diet containing 7.5% dried distillers grains with solubles (DDGS), 3) diets containing 7.5% soybean hulls (SBH), or 4) diet containing 7.5% citrus pulp. The experimental diets were fed for 4 wk in two phases (Phase 1: wk 1 and 2; Phase 2: wk 3 and 4). Intestinal tissue samples, liver samples, and blood samples were collected from a subset (n = 24) of the pigs on d 7, and blood samples were collected from another subset (n =24) on d 28 of the experiment. Dietary treatment had no effect on ADG, ADFI, or G:F throughout the experiment. Likewise, pig BW variability (CV), plasma IGF-I, or the plasma concentration of the acute phase proteins, a1-acid glycoprotein and haptoglobin, were not affected by dietary treatment. Real-time RT-PCR analysis revealed that on d 7, pigs fed DDGS had a greater (P < 0.05) relative abundance of Interleukin-6 and Interleukin-1 Beta mRNAs in ileum tissue. The d 7 mRNA expression of cytokines was not altered in jejunum, colon, or liver tissue by dietary treatment. Pigs fed diets containing 7.5% SBH had greater (P < 0.05) jejunum IGF-I mRNA expression, but expression of proglucagon was not affected by dietary treatment on d 7. Western blot analysis found no effect of dietary treatment on the abundance of phosphorylated-S6K in jejunum, ileum, or colon tissue on d 7. These results indicate that feeding 7.5% of a fiber source as DDGS, SBH, or citrus pulp did not affect the growth performance in weanling pigs, and that feeding DDGS alters the expression of cytokines in intestinal tissue. The lack of an increase in phosphroylated-S6K suggests other pathways for intestinal hypertrophy in response to dietary fiber.